The present invention relates to the use of UV initiators to polymerize (meth)acrylate-based monomers.
The manufacture of hydrogel contact lenses requires a careful balancing of numerous physical properties. For example, a hydrogel contact lens must achieve a certain minimum desired water content. The water content in combination with the chemical composition of the hydrogel material affect the potential oxygen permeability of the material. Without adequate access to oxygen, the cornea, which depends upon direct contact with environmental oxygen for its oxygenation, will become irritated and sustain damage. Therefore, oxygen permeability is important.
Equally important, for a lens to be worn comfortably on the eye, it must have the proper "feel". Many factors contribute to a clinically comfortable lens which has the proper "feel". Modulus is a measure of the material's stiffness. A lens material with a high modulus value will result in a lens which is too stiff to be worn comfortably. However, a lens having a low modulus value, and which is too "soft", may be easily damaged and cannot be easily handled during insertion into, and removal from the eye.
Making the lens sufficiently durable can therefore impact directly on the comfort of the lens in terms of raising the modulus value. The tear strength of the lens must be high enough for the lens to endure the necessary rigors of lens maintenance including cleaning, disinfecting, etc. Unfortunately, when one attempts to lower the modulus of a hydrogel material by known methods, the tear strength also drops. Similarly when one attempts to increase a hydrogel's durability by increasing the tear strength using known methods, the modulus also often increases, making the hydrogel lens material too stiff to be worn comfortably.
Modulus and tear strength may be adjusted by changing the relative concentrations of components known to affect those specific physical properties. In arriving at an acceptable hydrogel contact lens formulation, a balance is usually struck between acceptable, although not ideal, modulus and tear strength values. This balance often results in hydrogel lens materials which have an average comfort in terms of modulus and average durability in terms of material tear strength.